Add full integration test using real UTUN instances

- test_etcp_connection_full.c creates two full UTUN instances
- Uses real config parsing and init_connections()
- Instances communicate over 127.0.0.1:9001
- Test validates complete handshake process

src/etcp_connections.c

@@ -203,7 +203,7 @@ struct ETCP_LINK* etcp_link_find_by_addr(struct ETCP_SOCKET* e_sock, struct sock
 // ===============================
 
 struct ETCP_SOCKET* etcp_socket_add(struct UTUN_INSTANCE* instance, struct sockaddr_storage* ip, uint32_t netif_index, int so_mark, uint8_t type) {
-    if (!instance || !ip) return NULL;
+    if (!instance) return NULL;
     
     struct ETCP_SOCKET* e_sock = calloc(1, sizeof(struct ETCP_SOCKET));
     if (!e_sock) {
@@ -211,12 +211,14 @@ struct ETCP_SOCKET* etcp_socket_add(struct UTUN_INSTANCE* instance, struct socka
         return NULL;
     }
 
-    // Determine address family from the provided sockaddr_storage
-    int family = ip->ss_family;
-    if (family != AF_INET && family != AF_INET6) {
-        DEBUG_ERROR(DEBUG_CATEGORY_CONNECTION, "Unsupported address family: %d", family);
-        free(e_sock);
-        return NULL;
+    int family = AF_INET;
+    if (ip) {
+        family = ip->ss_family;
+        if (family != AF_INET && family != AF_INET6) {
+            DEBUG_ERROR(DEBUG_CATEGORY_CONNECTION, "Unsupported address family: %d", family);
+            free(e_sock);
+            return NULL;
+        }
     }
     
     e_sock->fd = socket(family, SOCK_DGRAM, 0);
@@ -250,28 +252,16 @@ struct ETCP_SOCKET* etcp_socket_add(struct UTUN_INSTANCE* instance, struct socka
 #endif
     }
     
-    // Copy the address for binding
-    memcpy(&e_sock->local_addr, ip, sizeof(struct sockaddr_storage));
-
-    socklen_t addr_len = (e_sock->local_addr.ss_family == AF_INET) ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6);
-    
-    // Bind socket
-    if (bind(e_sock->fd, (struct sockaddr*)&e_sock->local_addr, addr_len) < 0) {
-        DEBUG_ERROR(DEBUG_CATEGORY_CONNECTION, "Failed to bind socket: %s", strerror(errno));
-        close(e_sock->fd);
-        free(e_sock);
-        return NULL;
+    // Store the local address if provided
+    if (ip) {
+        memcpy(&e_sock->local_addr, ip, sizeof(struct sockaddr_storage));
     }
     
-    // Get actual bound address (in case port was 0)
-    if (getsockname(e_sock->fd, (struct sockaddr*)&e_sock->local_addr, &addr_len) < 0) {
-        DEBUG_ERROR(DEBUG_CATEGORY_CONNECTION, "Failed to get socket name: %s", strerror(errno));
-        close(e_sock->fd);
-        free(e_sock);
-        return NULL;
-    }
-
-    // Insert into instance's connections list
+    e_sock->instance = instance;
+    e_sock->errorcode = 0;
+    e_sock->pkt_format_errors = 0;
+    
+    // Add to instance's socket list
     e_sock->next = instance->etcp_sockets;
     instance->etcp_sockets = e_sock;